What was the SIZE of the Brown Owl-like bird you saw in South Dakota?

Flammulated Owl: Small owl with two color morphs (gray-brown and rufous) with many intermediate forms. The head has very small ear tufts, and dark eyes surrounded by rust-brown, pale-gray facial disk, and white eyebrows that start at the bill. It is the only small owl with dark, not yellow, eyes.

Northern Hawk Owl: Medium-sized, slender owl with white-spotted brown upperparts and brown-barred white underparts. The gray facial disk is partially bordered by a thick, brown stripe that extends to the upper breast; lacks ear tufts. Wings are long and relatively pointed. Tail is long and rounded.